The present invention relates generally to the field of electronic data storage and retrieval. In particular, the present invention relates to a bottom shield design of a magnetoresistive reader that eliminates magnetic interactions between the magnetic read head bottom shield and a magnetic read element by preventing displacement of any of a plurality of domain walls within the bottom shield.
A magnetic read head retrieves magnetically-encoded information that is stored on a magnetic medium or disc. The magnetic read head is typically formed of several layers that include a top shield, a bottom shield, and a read element positioned between the top and bottom shields. A resistance of the read element fluctuates in response to magnetic fields emanating from the rotating magnetic disc when the read element is positioned near the magnetic disc. The change in resistance of the read element can be detected by passing a sense current through the read element and measuring a voltage across the read element. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
During a read operation, the top and bottom shields ensure that the read element reads only the information stored directly beneath it on the magnetic medium or disc by absorbing any stray magnetic fields emanating from adjacent tracks and transitions. Within the bottom shield exists a plurality of magnetic domains. The magnetic domains are separated by one of a plurality of magnetic domain walls. Each domain has a magnetization that is oriented in a direction different than the magnetization of all adjacent domains. The application of an external magnetic field to the bottom shield can cause the magnetization of each of the domains to rotate, thereby causing the domains to move, grow or shrink. Thus, the domain walls are relocated due to the external magnetic field. This movement of a domain wall through a portion of the bottom shield that is directly beneath the read element causes a local perturbation of the spin structure within the read element and, therefore, produces an unwanted change in the resistance of the read element.
Until recently, the noise induced by domain wall movement has been negligible. But as storage densities on magnetic media and discs have increased, the reads elements have necessarily become smaller, more sensitive, and also more susceptible to noise created by domain wall movement. Therefore there is a need for a bottom shield design that prevents domain wall movement.